Simulated stereo sound system



United States Patent [111 3,548,101

{-72} Inventor Ramzi A. Shamma 56] References Cited 351 Broad St. Apt. 8-1206, Newark, NJ. UNITED STATES TS 2Y5; 33 32 3,299,208 1/1967 Driemeyer 179/l(3PS) [45] patented 7 3,296,376 1/1967 Svorec.. 179/1 (3P5) 2,114,680 4/1938 Goldsmith 179/!(3PS) Primary Examinerl(athleen H. Claffy Assistant Examiner-Randall P. Myers At!orney-Hopgood and Calimafde SIMULATEDSTEREO SOUNDSYSTEM ABSTRACT: A simulated stereophonic system for audio 4 claims6brawing Figs reproduction which employs a monaural amplifier and [52] US. Cl.. 179/1 wit hing selector means connected to the output of the am- [51] lnt.Cl H 41 3/12 plifier to alternately feed either a left speaker or a right [50] Field of Search 179/13, speaker, while an output is being continuously supplied to a 1.3PS, 1.3A center speaker.

PM! (/P /6 Pz- 444/ flap IMAM/5e flfilPL/F/E? 6 A4 624 x942 Sir/raw; JmzF/zz 32222742 SIMULATED STEREO SOUND SYSTEM BACKGROUND OF THE INVENTION Present day commercial sound reproduction systems generally fall into two categories. One of these is the monaural system which has a single amplifier channel, and the other is a stereophonic system which employs two channels, each being separate from the other and connected to its own separate speaker. The stereophonic system is superior to the monaural system since the effect produced is more live, i.e., it more closely resembles that heard in the presence of an actual orchestra. The stereophonic system, however, does have the disadvantage of being much more expensive'than the monaural system since approximately twice as many parts are used as in a comparable monaural system. Also, although the stereophonic system does achieve excellent performance, in its conventional design it is generally limited to pure or faithful reproduction of the music so that other desirable musical effects are not produced.

OBJECTS OF THE INVENTION One of the objects of this invention is to provide a musical system using a monaural amplifier which will reproduce music in a simulated stereo manner, so thatit creates an illusion of live music as distinguished from musical reproduction from a single-point source.

A further object of the invention is to produce an entirely different type of musical effect than that heretofore known.

A still further object is to provide 'a' sound system which produces a stereophonic effect from a monaural or single channel amplifier.

Yet another object is to provide a system capable of creating a new and pleasing musical effect from a monaural amplifier unlike that heretofore known. t

A still further object is to provide a stereophonic effect by means of equipment costing only a fraction of that required for a comparable stereophonic system.

BRIEF DESCRIPTION OF THE DRAWING a F IG. 1 is a block diagram which illustrates a sound reproduction system according to theprinciples of this invention;

FIG. 2 illustrates one schematic wiring diagram for a sound reproductionsystem of the type seen in FIG. 1;

FIG. 3 shows one form of a first relay employed in the system of FIGS. 1 and 2 in accordance withthe principles of this invention; and

FlGS. A, 48 and 4C show one form of a second relay employed in the system of FlGS. l and 2 in accordance with the principles of the invention, FIG. 4A being a side view, FIG. 48

being a top view when the relay is deenergized, and FIG. 4C

being a top view when the relay is energized.

SUMMARY OF THE lNVENTION Briefly, this invention includes a monaural or single channel amplifier for reproducing music or other program material which has its output directly connected to a center loudspeaker. A control amplifier is also provided with a switching selector comprising a pair of sequentially operable relays and connected to the output of this amplifier. The input of the control amplifier is connected to receive a signal from the single channel amplifier and the control amplifier operates the relays of the switching selector in response to the program signal variations. When operated, the switching selector connects the output of the monaural amplifierto either a left speaker or a right speaker, in accordance with variations in the voltage existing in the system which are representative of the program being reproduced.

DESCRIPTION OF PREFERRED EMBODlMENT Referring now to FIG. 1, there is provided a monaural or single channel high-fidelity amplifier comprising a preamplifier 10 and a power amplifier 12. The input of the preamplifier 10 is connected to a pickup device 14 which may be a monophonic record playback cartridge for cooperating with a record 13, or may be a tape head or other pickup device. An output line 16 is connected to the power amplifier output and feeds the output voltage via a line 16a to a center loudspeaker 18.

In accordance with the principles of this invention, a control amplifier 20 is also provided and receives a signal from the single channel amplifier via line 22. This signal is amplified by the control amplifier 20 and fed to a switching selector 24 which is connected to the control amplifier 20. The switching selector 24 is connected via a line 16b between the output line 16 from the power amplifier 12 and a pair of loud speakers 25 and 26. The speaker 25 is positioned to the left side of the center speaker 18 and the speaker 26 is positioned to the right side of this center speaker. The switching selector 24 operates in a manner, more fully e described below, whereby the left speaker 25 receives a signal from the power amplifier 12 for a period of time and at a later time the right speaker 26 then receives the signal for another period of time, depending upon the content of the recorded musical program. The time intervals during which these speakers operate depend upon the particular makeup of the musical program being reproduced by the system. The center speaker 18 is always on in combination with either the left speaker 25 or the right speaker 26 to produce the overall musical effect.

In accordance with this invention, anew musical efiect is produced which is neither the conventional monaural speaker point source type of reproduction, nor the multispeaker source single-channel-type production whereby two speakers are simultaneously actuated from a single amplifier channel, nor the conventional two channel stereophonic system whereby two speakers are employed and are also operated simultaneously. Instead, an entirely new musical effect is created which utilizes a center speaker in combination with speakers to the left and right thereof whereby a listener continually hears music from the center speaker but the music from the left and right speakers alternately shifts first from one to the other and then back again, depending upon the musical content of the particular program.

FIG. 2 shows one schematic wiring diagram for the sound reproduction system of HG. 1. In this figure similar numbers designate similar parts as in FIG. 1. The preamplifier l0 and power amplifier 12 may be any conventional type and although tubes are employed in the various circuits shown in FIG. 2, it will be clear that transistor circuits can also be used. In customary manner, the pickup 14 is connected to the input of the preamplifier 10 with the output thereof connected to the power amplifier 12. Volume, bass and treble controls 30, 32 and 34 respectively are also provided for adjusting the response of the system as desired. An output transformer 36 is provided to deliver power from the power amplifier 12 to the speakers 18, 25 and 26. A control 37 is provided to adjust the output level of the center speaker 18 relative to the side speakers 25 and 26.

The control amplifier 20 in the particular illustrative embodiment shown includes a triode amplifier tube 38 and a pentode amplifier tube 56. The grid 40 of the tube 38 is connected through a diode 42 and the line 22 to receive a signal from the output of the preamplifier 10. A variable grid resistor 44 and a capacitor 45 bridging this resistor are: connected between the grid 40 and chassis ground. A variable cathode resistor 46 is provided between chassis ground and the cathode 41. A plate load resistor 48, also variable, is connected between the plate 43 of the tube 38 and a source of 13+ potential in the power supply 28, to develop an output signalfor application to the grid of the next tube 56.

A coupling capacitor 52 transfers this signal from the plate load resistor 48 to the grid 58 of the p'entode tube 56. A grid resistor 54 is provided between the grid 58 and ground. A sensitivity control 62 in the form of a potentiometer 62, bridged by a capacitor 64, is connected between the cathode 60 of the tube 56 and ground. The function of this sensitivity control will be covered later in the description.

Further referring to FIG.'2, the switching selector 24 includes a first relay 71 and a second relay 72. The relay 71 has an operating coil 102 connected between the plate 66 of the tube 56 and the B+ source of potential for the plate. A capacitor 110' is connected between the armature 108 of the relay 7] and ground. This armature 108 is also connected to a resistor 134. This resistor is placed in the high voltage current return lead, via wire 137, between chassis ground and the high-voltage secondary center tap 139 on the transformer 138 of the power supply 28. The resistor 134 is bridged by a capacitor :136'and these together form an RC circuit, the importance the contact 146 is connected to the right speaker 26 via wire FIG. 3 illustrates the first relay 71 in greater detail. From 3 this figure it will be seen that the stationary contacts 104 and 106 are made adjustable by means of screws 112 and 114 respectively. The armature 108 is held in the position furthest aaway from the soft iron core 116 by means of a spring 118 connected to a bracket or other means 120 mounted on the relay base 122. The armature 108 is held on a shaft 124 so that when the armature moves this shaft will rotate very slightly. 1 This shaft 124 is provided with generally V-shaped ends for mountingain cup-shaped supports. One of these supports is indicated by the numeral 126 and may be rotated by means of the screw 128 to provide a fine tightening adjustment of the shaft 124, whereby the armature 108 may be adjusted to move in a slightly damped condition.

FIGS. 4A, 4B and 4C illustrate the second relay 72 in greater detail, where it will be seen the coil 140 is mounted on a suitable base 152 and wound about a soft iron core 154. A magnetic plate 156 is mounted for movement about a pivot 158. The upper end of the magnetic plate 156 is arranged to engage an aperture 160 in a top plate 162. This top plate 162 is arranged to move to the right when the relay is energized as seen in FIG. 4C. When the relay 72 is deenergized, the top plate 162 is returned to the position shown in FIG. FIGS. 4A

. and 48 by means of a tension spring 164 attached to the top plate. At the right end of the top plate 162 there is provided a downwardly extending projection 168 for engaging the armature 142. The armature 142 is mounted for clockwise and counterclockwise rotation about the axis of a pivot 170. Rotation of the armature 142 in either the clockwise or counterclockwise direction of rotation results from engagement of the pin 168 on either the curved surface 172 or 174 when the top plate 162 moved to the right upon energization of the relay.

' When the top plate returns to its deenergized position to the left under the action of the spring 164, the armature 142 main- 7 tains the position to which it was previously set by the pin 168 to engage one of the contacts 144-146 and only engages the The system of this invention operates in the following manner. Referring first to FIGS. 1 and 2, when the record 13 is I- -.being played, the electric signals generated in the pickup 14 are amplified in the usual manner in the preamplifier 10 and w the power amplifier Y12 and are fed directly to the center wwspeaker l8. Either the left speaker 25 or the right speaker 26 are also operating simultaneously since one of these speakers ',is always functioning with the center speaker 18. Whether the left speaker 25 or right speaker 26 is on depends on the posi- 5 tion of the armature 142 of the second relay 72.

For purposes of explanation, let it be assumed that the system has just been turned on and that the record 13 has just 1;; started to play. Also let it be assumed that the recorded music signal level is low so that neither the first relay 71 nor the second relay 72 has yet been actuated. Thus, the top plate 162 and armature 142 will be in the positions shown in FIG. 4B, with the contact 146 engaged by this armature so that the right speaker is presently connected. Thus the listener 'will presently hear the right speaker 26 and the center speaker 18.

As the music continues,z.a varying signal potential will of, course exist throughout the'system. The diode 42 rectifiesthesignal on the line 22 so that a negative potential of varying am-. plitude is impressed on the grid 40 of tube 38. This negative signal potential is amplified by theutubes 38 and 56, causing a potential to be impressed acrossthe coil 102 of the relay 71. This first relay 71, however, will not close until the potential across the coil 102 reaches a given threshold level for-which the system is previously adjusted.

Now when the recorded music signal level reachesor exceeds a value which produces this given threshold level across the coil 102, the first relay 71 will close. This causes the armature 108 of relay 71 to engage the contact 104, see FIGS. 2 and 3, causing the voltage on the line 137 to be impressed across the coil of the second relay 7 2. In the particular circuit under consideration, the voltage on this line 137 has a value of 17 volts and represents the potential across the resistor 134 and the capacitor 136.

When the second relay closing voltage of 17 volts is impressed on the coil 140, the magnetic plate 156 is attracted to the coil l40.-This moves the top plate 162 to the right against the tension force of the spring 164. This causes the pin 168 to engage the curved surface 172, which rotates the armature 142 in a clockwise direction from the position seen in FIG. 48, to that seen in FIG. 4C. Thus the armature 142 disengages the contact 146 and engages the contact 144 which switches the output of the transformer 36 on line 16b from the right speaker 26 to the left speaker 25.

The armature 142 will now maintain the position seen in FIG. 4C for an indefinite period of listening time. The listener will now hear the center speaker 18 and the left speaker 25.

Now it is important in order to produce the most pleasing musical effect, that the relay 72 be rendered incapable of immediately switching the right speaker 25 back on if the recorded music signal level should happen to immediately drop to a very low value. This is accomplished by maintaining the armature 142 in its new clockwise rotated position by the particular design of the relay 72. Thus if the recorded music signal level now decreases below that sufficient to maintain the first relay 71 closed, the contact 104 of the first relay 71 will open, thus deenergizing the second relay 72. This causes the spring 164 on the second relay 72 to move the top plate 162 to the left so that the pin 168 now disengages thearcu'ate surface 172 of the armature 142 and this armature will maintain its position seen in FIG. 4C until the relay 72 is again energized. Such energization will not occur, however, until the recorded music content again reaches the threshold level sufficient to close the first relay 71. When this happens, the second relay 72 will again be energized, causing the top plate 162 to again move to the right. This time, however, the pin 168 will engage the curved surface 174 since when the armature 142 was moved to the clockwise position earlier, the tip 176 of the armature 142 was moved to a position placing this surface 174 in line for engagement-by this pin on'the next excursion of the top plate 162. Consequently, the armature-142 is now returned in a counterclockwise direction about the axis of the pivot to again engage the contact 146 to switch the output from the left speaker 25 back to the right speaker26. Accordingly, the listener will now again hear the center speaker 18 and the right speaker 26.

As the music continues to play, the music signal level will again drop at some point to a level sufficient to release the relays 71 and 72, causing the top plate 162 of the relay 72 to again return to its rest position. After this when the music signal level causes the relays 71 and 72 to again become energized, the top plate 162 will once more rotate the armature 142 clockwise to engage the contact 144 once more removing the output signal from the right speaker 26. and feeding it to the left speaker 25. The process continues indefinitely in this manner so long as the music continuesll have discovered that the shifting of the musical program" from one of the side speakers to the other and back again in the manner described imparts a live and dynamic characteristic to the listener that results in a very pleasant musical experience.

The switching between the left and right speakers 2526 depends on a number of factors. These factors include the music signal level or amplitude, the frequency of occurrence of changes in the signal amplitude above, and below the threshold level, time, and the mechanical'characteristics of the relays. The effect of the variations in the music signal level or amplitude on the switching has already been discussed at some length in connection with the operation of the first and second relays 71 and 72. e

The switching as a result of the frequency of occurrence of the changes in signal amplitude above and below the threshold level depends on several things. One of these is the action of the armature 108 of the first relay 71, which in turn is affected by the distance that it must travel from its deenergized position to engage the contact 104. Both the screw 112 which carries the contact 104, and also the screw 114, affect the action of the annature 108. For example, a greater potential is required to attract the armature 108 when the screw 114 is set so that the armature is further from thecore 116. The action of the armature 108 is also affected by the armature damping adjustment screw 128 and this screw may be tightened to increase the stiffness of the armature movement to make it less responsive to minor variations in the music signal which are too frequent. Also in connection with the frequency of occurrence of the changes in this signal amplitude, it should be observed that the number of shifts of the power amplifier output between the left and right speakers 25 and 26 is reduced by the one way" action of the second relay top plate 162. As noted above, the relay 72 changes the output from one side speaker to the other when the signal level drops below and is then raised above the threshold level. In other words, the signal does not shift from one side speaker to the other when there is a change merely above or below 'the threshold value.

In connection with the time factor, some further explanation is necessary. As already described, when the first relay 71 is closed, it energizes the second relay 72. when this second relay 72 is closed, it places the second relay 'coil 140 directly across the resistance 134. This resistance is bridged by the capacitor 136. Now the resistance 134 is selected so that the voltage drop across it is 17 volts and the relay 72 requires at least volts to actuate its armature 142.

Thus when the first relay contact 104 is closed, the second relay coil 140 starts to discharge the capacitor 136. The time it takes to reduce the voltage across the capacitor 136 to a given value depends on the resistance value of the coil 140, the resistance value of the resistance 134 and also the capacitance value of the capacitor 136. The time constant of these three elements 134, 136 and 140 is selected so that the voltage across them is reduced from l7 volts to less. than 15 volts in approximately 2 seconds. Therefore, ifthe relay 72 has been closed for approximately 2 seconds and musicprogram signals are then produced which rapidly decrease and then increase above and below the threshold level several times in a relatively short time interval, the relay 71 will operate, but the relay 72 will not operate. This is because when the relay 71 has released 'relay 72 with the first reduction in signal level, the a capacitor 136 will not have had sufficient time to recharge to the operating potential necessary to actuate the relay 72. After discharging for 2 seconds from the l l-volt condition, it requires approximately 1 second for the capacitor 136 to recharge sufficiently to operate the relay.72.- In this manner rapid shifting of the program from one side speaker to the other is avoided after a period of reproduction from one of these speakers. i

The time constant of the RC combination 134, 136, 140, is further selected so that if the relay 7'1 closes several times in rapid succession for say, one second each, the capacitor 136 will discharge through the coil 140 quickly enough to reduce the potential thereon below that necessary to operate the relay 72. Thus, continuous rapid shifting of the program from one side speaker to the other is also avoided after several fairly rapid shifts have occurred.

The above-described restrictive or limiting action imposed on the relay 72 prevents an annoying rapid fire type of transient condition switching between the left and right speakers 25, 26 and produces instead a slower rate switching action having very pleasant listening characteristics.

The mechanical characteristics of the first and second relays 71 and 72 are also very important .in the operation of the system. The effect on the first relay adjustment screws 112 and 114 has been mentioned above. Also reference has already been made to the elimination of undesirable switching by means of adjusting the operating stiffness of the armature 108 of the first relay 71. The elimination of such undesirable switching is also aided by the inertia of the operating mechanisms of both relays 71 and 72 and the time it takes the second relay top plate 162 to travel its :full length to actuate the armature 142.

in order to achieve proper operation of the system so that the most desirable and pleasing switching action between the side speakers can be produced, the resistors 44, 46 and 48 are made adjustable and the potentiometer 62 is provided as a sensitivity control. This sensitivity control is provided with a knob convenient for the listener to adjust the operational sensitivity of the relay 71 whereby a wide range of switching variation may be achieved, according to the listener's personal taste. This wide range of switching variation capability with the sensitivity control 62 is set by factory adjustment of the variable resistors 44, 46 and 48 and once these adjustments are made, only minor variations are needed to compensate for aging and replacement of components.

It will be appreciated that a numberof the components in the system are critical per se or are critical with respect to other components. Among these of course are the relays 71 and 72, and the capacitor 46 which I have found satisfactory at a value of .25 pf. Also critical are the value of the resistor 134 and the time constant of the RC combination l34136 with the relay coil 140. In this connection 1 have satisfactorily employed a value of 250 ohms for the resistor 134 and 750 pf. for the capacitor 136 in connection with the relay 72 having the operating characteristics described above. Also the relays 71 and 72 can, if desired, be replaced by a single-relay unit which incorporates the necessary functions. Furthermore, the control amplifier 20 can be substantially simplified, as by eliminating one of the tubes 38, 56 when very sensitive relays are employed. It is also to be noted that :if the base, treble and volume controls 30, 32 and 34 are provided in the preamplifier 10, their settings will affect the switching operation.

It will of course be apparent that while the invention has been described in connection with recorded music as the program source, that this invention is useful for other types of programs including nonmusical programs and live broadcasts. It will also be appreciated that the advantages of this invention and the novel character of the sound made possible thereby can be achieved by the use of twospaced speakers connected to the switching selector, without the use of the center speaker employed in the description above.

While the foregoing description sets forth the principles of the invention in connection with specific apparatus, it is to be understood that the description is made only by way of example and not as a limitation of the scope of the invention as set forth in the objects thereof and the in the accompanying claims.

1 claim:

1. A system for the simulation of stereophonic sound from the reproduction of monaural sound comprising:

monaural pickup means;

a single channel amplifier for receiving monaural signals from said monaural pickup means;

loudspeaker means for reproducing said monaural sound comprising a center loudspeaker connected to said amplifier for continual reproduction of said monaural sound, and left side and right side loudspeakers connected to said amplifier for alternatively reproducing said monaural sound simultaneously with said center speaker;

switching means coupled between said side loudspeakers and said amplifier for switching the output of said amplifier from one side speaker to the other; and

actuating means connected to receive said monaural signal for controlling the operation of said switching means in response to the amplitude level of said monaural signal, whereby the sound is switched from one side loudspeaker to the other at a predetermined amplitude level in order to provide simulated stereo sound 2. The system of claim 1 wherein:

said switching means includes an adjustment for modifying the predetermined amplitude level;

adjustable mechanical damping means to control the responsiveness of operation; and

means to provide switching operation only when the amplitude level is increasing in value.

3. The system of claim 2 including electrical time delay means connected to said switching means for preventing the operation of the switching means until the amplitude level has remained below the predetermined value for a preset time period.

4. The system of claim 3, wherein said actuating means includes a sensitivity control adjustment whereby the listener can change said predetermined level and thus obtain a wide range of switching variation according to his personal taste. 

